OpenGL iOS屏幕坐标到场景坐标

Question

I'm using OpenGl to make a little Application and I have no idea how to get the x , y and z coordinates of a touch

For example:

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
CGPoint touchPoint = [touch locationInView:[self view]];

float X = touchPoint.x;
float Y = touchPoint.y;

}

with this I only get the x and y coordinates ,but I need the z as well

Answer 1

You can't read the z buffer on OpenGL ES. When I've needed to do this kind of 3D hit testing I've projected a 3d line through the scene and done the hit-testing myself.

For OpenGL on Retina devices you need to multiply x and y by the scale. To support iPhone 6+ you need to use nativeScale when available.

// Do this when setting up view controller and remember theScale.
if ([[UIScreen mainScreen] respondsToSelector:@selector(nativeScale)])
  theScale = [[UIScreen mainScreen] nativeScale];
else if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)])
  theScale = [[UIScreen mainScreen] scale];
else 
  theScale = 1.0;